Modified heat pipe for phase change cooling of electronic devices

ABSTRACT

Exemplary embodiments provide a heat pipe including a flexible chamber that is capable of expanding, compressing and/or restoring. In one embodiment, the heat pipe can include a hollow metal casing including a pipe structure connected to an expandable chamber at one end of the pipe structure. The other end of the pipe structure can include an evaporating section for receiving heat and the expandable chamber can include a condensing section for releasing the heat. The expandable chamber can be configured to change in volume to control one or both of a temperature and a pressure in the hollow metal casing. The heat pipe can also include a capillary system arranged at an inner surface of the hollow metal casing that includes the pipe structure and the expandable chamber.

DESCRIPTION OF THE INVENTION

1. Field of the Invention

This invention generally relates to heat transfer components and, more particularly, to heat pipes that include an expandable chamber.

2. Background of the Invention

The power density of components used in portable electronics such as cellphones, MP3 players and global positioning systems (GPSs) is increasing as more features are added to the equipment and with the advent of new package technologies such as stacked die, stacked packages, and through-silicon vias (TSV) packages. Additionally, new battery technologies have increased the power capacity, e.g., by about 10% per year. Due to these reasons, the operating temperature of portable electronic devices has increased dramatically. However, due to battery life concerns, these portable electronic devices do not use miniature fans and heat sinks.

Conventional methods to release the increased heat generated by these devices include the use of heat spreaders, which are either integrated into the printed circuit board (PCB) or distributed on top of the package. For example, the heat spreader may be an external casing having high thermal conductivity, often simply a copper plate, designed to cover an electronic device and conduct heat to a dissipating surface. Heat is removed from the dissipating surface through either conduction into the user's hand or convection and radiation into the environment.

Other cooling schemes which have been explored include the use of phase change materials to absorb heat generated from an activity or operation such as a phone call. The absorbed heat is then gradually released during the quiescent time between calls by cooling down and changing phase. For example, a mass of paraffin or low melting temperature salt might be encased around the component to be cooled. As the component heats, the phase change material melts, transforming the heat from a temperature rise to a phase change event. The phase change material also is provided with thermal conduction to heat dissipative surfaces such that when the heating cycle such as a phone call completes, the phase change material cools, changing back into a solid before the next heating event.

A structure which is commonly used to conduct heat from a heated component to the dissipative surface in computers is a heat pipe. A heat pipe consists of a tube coated on the inside with a wicking structure. The heat pipe is partially filled with water and the pressure inside is reduced to tune the boiling point of the water to a desired temperature which becomes the operating temperature of the heat pipe. The heating end of the heat pipe is attached to the hot component. The cooling end of the heat pipe is attached to the heat dissipating surface, often a heat sink. When the temperature of the heated end reaches the boiling point of the water inside, the water absorbs the heat needed to vaporize, fills the tube with vaporized water, which then re-condenses at the cooled end of the heat pipe. The heat of vaporization is given up during the condensing process. The now liquid water is pulled by capillary action back to the hot end of the pipe.

SUMMARY OF THE INVENTION

Applicant has realized that new heat pipes and methods are needed to have an increased cooling capacity so as to release the increased heat generated by components used in, for example, portable electronics with increased power density and/or increased power capacity.

Conventional cooling devices, such as heat spreaders, have low cooling capacity. For example, when heat spreaders are used, the total power dissipation of the hand held system is about 3 watts due to the cooling capacity of the hand. Conventional heat pipes use low volumes of phase change materials, such as water, and have low stand alone cooling capacity. A common failing of conventional heat pipes is dry-out of the water. That is, the water boils away from the hot end of the pipe faster than it re-condenses at the cold end.

Thus, there is a need to overcome these and other problems of the prior art and to provide a new heat pipe construction to minimize heat pipe dry-out, to provide more phase change working fluid volume to handle higher power peaks, and to integrate the heat sink onto the heat pipe in a compact structure intended for portable electronic devices. The new heat pipe can have increased stand alone cooling capacity as compared with conventional heat transfer components used in the art.

In order to develop such heat pipe, the Applicant incorporated an expandable chamber into a conventional heat pipe, such as a conventional cylindrical heat pipe. In one embodiment, the discovered expandable chamber can be connected to one end of a pipe structure and can have flexible corrugations so that the volume of the expandable chamber can increase or decrease. The incorporation of the inventive expandable chamber can be used to control internal pressure and boiling point of a working fluid or a phase change material flowing within the heat pipe. The incorporation of the inventive expandable chamber can allow for a large quantity of the working fluid or the phase change material to enable more peak power heat dissipation through its boiling.

Preliminary experiments and calculations have been performed to analyze the inventive heat pipe having the expandable chamber. For example, water, having a latent heat of vaporization of about 2300 J/gm, can be used as a working fluid or a phase change material. As known, a watt represents about 1 J/sec. A phone call that runs 3 watts for 8 minutes (i.e., 480 seconds) can therefore represent 1440 joules. This energy is sufficient to boil only 0.6 gm of water.

In the case when 1 gm of water (i.e., 1 cc, or 1000 mm³) is used, the disclosed heat pipe can handle a 3 watt power peak for 13 minutes by boiling alone. Water having the volume of about 1000 mm³ (i.e., 1 gm) can be filled in an exemplary heat pipe having a cross sectional area of about 100 mm² with an initial length of about 10 mm, which however can be extended to be, e.g., about 40 mm to about 80 mm, which allows for a large volume of vapor to fill the heat pipe. It should be noted that as the vapor chamber expands, the internal pressure will also be increasing, raising the boiling point of the working fluid. The electronic system into which the exemplary vapor chamber will be placed must allow for adequate cooling of the chamber to allow the boiling temperature of the fluid to remain below the maximum allowed operating temperature of the electronic device, which is often 85° C. or 105° C.

In one experiment, the larger volume of water can absorb excess heat energy as the temperature of related electronic devices goes above 65° C. Water boils at 65° C. at a pressure of −3.8 psi. In the example where the cross sectional area of the expandable chamber is about 100 mm² (i.e., about 0.155 in².), the expandable chamber may have spring-type mechanism to produce a weight of about 1.58 lbs against the atmospheric pressure of about 14 psi in order to obtain the pressure of about 3.8 psi required to boil water at 65° C.

In this manner, the inventive heat pipe can provide an increased cooling capacity by allowing a higher volume of working fluid, the water. The expanding chamber can act to maintain a lower pressure as the water boils while at the same time can perform the function of a heat sink to re-condense the water. Conventional heat pipes allow only minimal change in volume and have fixed physical dimensions that are dependent on only the thermal expansion constants of the materials. As a result, large volume of working fluids, such as water, cannot be used to absorb excess heat energy in conventional heat pipes.

Additionally, the disclosed heat pipe having an expandable chamber connected to a pipe structure can provide flexibility in assembly. For example, the pipe portion can be bent around curves to fit the contours of related electronic systems and the expandable structure portion can be flattened to fit any flat-like volume.

Further, the inventive heat pipe having expandable chambers can be very compact to enable cooling, e.g., in cell phones or other handheld applications and can be an enabler for high density stacked die components.

The technical advances represented by the invention, as well as the aspects thereof will become apparent from the following description of the preferred embodiments of the invention, when considered in conjunction with the accompanying drawings and the novel features set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principles of the invention. In the figures:

FIG. 1 depicts an exemplary heat pipe including an expandable chamber in accordance with the present teachings;

FIG. 1A depicts a cross sectional view of the exemplary expandable chamber of FIG. 1 in accordance with the present teachings; and

FIG. 2 depicts the exemplary heat pipe of FIG. 1 in an exemplary working state in accordance with the present teachings.

It should be noted that some details of the FIGS. have been simplified and are drawn to facilitate understanding of the inventive embodiments rather than to maintain strict structural accuracy, detail, and scale.

DESCRIPTION OF THE EMBODIMENTS

The Applicant has realized that a new heat pipe needs to be provided. In an exemplary embodiment, the inventive heat pipe can include an expandable chamber that can accommodate an increased volume of water, as compared to a conventional heat pipe. The increased volume of water can be used as the phase change material to control and improve heat dissipation. The increased volume of water can be used because the expandable chamber can increase one or more of its dimensions, for example, in an accordion-like manner. In contrast, conventional heat pipes have fixed physical dimensions. Applicants recognize that conventional heat pipes can change dimensions due to thermal expansion. However, the change in dimension due to thermal expansion is not sufficient to accommodate a larger volume of water to increase heat dissipation.

Reference will now be made in detail to the present embodiments (exemplary embodiments) of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

In the following description, reference is made to the accompanying drawings that form a part thereof, and in which is shown by way of illustration specific exemplary embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the invention. The following description is, therefore, merely exemplary.

Exemplary embodiments provide a heat pipe including a flexible vapor chamber that is capable of expanding, compressing and/or restoring. In one embodiment, the heat pipe can include a hollow metal casing including a pipe structure connected to an expandable chamber at one end of the pipe structure. The other end of the pipe structure can include an evaporating section for receiving heat and the expandable chamber can include a condensing section for releasing the heat. The heat pipe can also include a capillary system arranged at an inner surface of the hollow metal casing that includes the pipe structure and the expandable chamber. In an exemplary embodiment, the expandable chamber can be, for example, a spring type vapor chamber that increases or decreased in volume to control the heat pipe internal pressure and the boiling point of a working fluid, such as water, alcohol or their combinations, continuously flowing in the heat pipe. A larger quantity of water can then enable more heat dissipation through boiling.

In various embodiments, the expandable chamber can include, for example, corrugations that are flexible so that the volume of expandable chamber can increase or decrease. In various embodiments, the expandable chamber can include a cross sectional shape, such as, for example, a circle, a square, a rectangle, a triangle, or a polygon. Such cross sectional shapes can be, for example, shaped into folds to form corrugations along a main axis direction of the expandable chamber. In this case, the volume of the expandable chamber can thus be changed by folding or unfolding the corrugations.

In various embodiments, the expandable chamber can be expandable and restorable relative to an equilibrium state. In various embodiments, the expandable chamber can include a spring-type mechanism that further includes a linear or non-linear expansion and a linear or non-linear restoration. In various embodiments, the expandable chamber may or may not include a thermal expansion depending on the materials used for the chamber.

FIG. 1 depicts an exemplary heat pipe 100 in accordance with the present teachings. It should be readily apparent to one of ordinary skill in the art that the heat pipe 100 depicted in FIG. 1 represents a generalized schematic illustration and that other components can be added or existing components can be removed or modified.

As shown, the heat pipe 100 can include a metal casing 102. The metal casing 102 can include a pipe structure 124, e.g., having a cylindrical configuration, and an expandable chamber 116 connected at one end of the pipe structure 124. As used herein, the term “expandable chamber” refers to a chamber that can increase one or more of its dimensions because of the structural configuration of the chamber. In an exemplary embodiment, the structural configuration of the expandable chamber can be accordion-like. The other end of the pipe structure 124 can include an evaporating section 112 (also referred to herein as a heating section, or a heat absorbing section) which is connected to the electronic component 180 for receiving heat during a heat pipe operation, while the expandable chamber 116 can include a condensing section (also referred to herein as a cooling section, or a heat emitting section) for releasing the heat. Other embodiments can also include a condensing section covering a portion of the pipe structure 124, in addition to the covering of a portion or a whole of the expandable chamber 116. An adiabatic section 114 can be arranged between the evaporating section 112 and the condensing section.

Inside the metal casing 102 that includes the pipe structure 124 and the expandable chamber 116, the heat pipe 100 can further include a capillary system 104 and a vapor channel 106.

The metal casing 102 can be a hollow metal casing made of highly thermally conductive materials, such as copper, copper alloys, aluminum, or copper clad stainless steel. A working fluid, e.g., a volatile medium such as water or alcohol, can be contained in the metal casing 102. The capillary system 104 can include, e.g., a capillary wick structure known to one of ordinary skill in the art, and can be arranged in the inner surface of both the pipe structure 124 and the expandable chamber 116. In various embodiments, the capillary system 104 can include a wick material including, for example, braided Cu or sintered powdered Cu.

The vapor channel 106 can be surrounded by an inner surface of the capillary system 104 so as to guide the working fluid to flow therein during operation. The vapor channel 106 can be defined along an axial direction of the pipe structure 124 and extended into the expandable chamber 116. The vapor channel 106 can be located at a center of both the metal casing 102 and the expandable chamber 116.

As shown in FIG. 1, the metal casing 102, the capillary system 104 and the vapor channel 106 can have a conformable shape according to the shape of the pipe structure 124 and the expandable chamber 116. For example, portions of the metal casing 102, the capillary system 104 and the vapor channel 106 that are associated with the pipe structure 124 can have, e.g., a cylindrical shape corresponding to the shape of the pipe structure, while portions associated with the expandable chamber 116 can have expandable shapes corresponding to the shape of the expandable chamber 116 as illustrated in FIG. 1A. For example, FIG. 1A depicts a cross sectional view of the expandable chamber 116 of the heat pipe 100 of FIG. 1 in accordance with the present teachings.

The expandable chamber 116 that includes corresponding portions of the casing 102, the capillary structure 104 and/or the vapor channel 106 can exhibit an expansion and/or contraction action from its equilibrium state (also referred to herein as a rest state), for example, expanding in one or more axial directions of length, width, height, and/or volume; and can experience a partial or full restoration to its equilibrium state after the expansion and/or contraction.

For comparison, the device 100 of FIG. 1 shows an exemplary expandable chamber 116 in an equilibrium or rest state having an exemplary length L₀ in accordance with the present teachings. From this equilibrium state, the chamber 116 can be expanded, for example, along a length wise direction 150 or can be compressed along a length wise direction 155. The expandable chamber 116 can also be restored along direction 155 after the expansion. For example, FIG. 2 depicts the exemplary heat pipe 100 of FIG. 1 in an exemplary working state, wherein the expandable chamber is an expanded chamber 116 a in a length wise direction to have an expanded length L_(Expanded), where L_(Expanded) is greater than L_(D).

To accomplish the expansion, expandable chamber 116 can include, for example, flexible corrugations having various cross sections shaped into folds. The volume of expandable chamber 116 can then be increased (see 116 a) from its rest state by unfolding the folds. In the illustrated example of FIG. 2, the expanded chamber 116 a can have a circular cross section 132 unfolded at 134 to increase the volume of the chamber. Such expanded chamber 116 a can be capable of partially or fully restoring to its equilibrium state having a restored length close or equal to L₀ (see FIG. 1), wherein the exemplary circular cross section 132 of the flexible corrugations can be folded at 134.

In an exemplary embodiment, the expandable chamber 116 can have a spring-type mechanism, wherein the force (e.g., provide by the water vapor) required to expand the expandable chamber has a linear or non-linear relationship with the distance that the chamber has been stretched or compressed away from the equilibrium state. That is, the spring-type mechanism can include a linear or non-linear expansion and compression from equilibrium state and/or a linear or non-linear restoration to its equilibrium state.

In one embodiment, the expandable chamber 116 can have a force constant or a spring constant which is a function of the number of folds in the expandable chamber, the depth of the folds, the angle of the bends at the top and bottom of the folds, and the material of the chamber, all of which can be adjusted to control the heat pipe operation. The spring constant can be adjusted depending on the area and compressed length of the expandable chamber 116 to maintain a predetermined boiling temperature for the water inside the chamber. For example, water at one-quarter of normal pressure can boil at about 65° C., while water at one-tenth of normal pressure can boil at about 45° C. One of ordinary skill in the art will understand that by adjusting the spring constant of the expandable chamber 116, the boiling point can be tuned to give the best thermal performance for the electronic system. One of ordinary skill in the art will also understand that the spring constant of expandable chamber 116 can be adjusted in a variety of ways including, but not limited to, adjusting the thickness and/or cross sectional shape of the walls of the expandable chamber, changing the material composition of the walls of the expandable chamber, changing the number of folds in the expandable chamber, changing the depth of the folds, or other adjustments. In various embodiments, a separate spring may be inserted in the expandable chamber to accommodate the controlled boiling pressure or to stop the expansion at a fixed length.

In various embodiments, although the chamber 116/116 a in a direction perpendicular to the main direction of the pipe structure 124 is shown having a round cross sectional shape in FIG. 1, one of ordinary skill in the art will understand that other regular or irregular cross sectional shapes can be used including, but not limited to, square, rectangle, triangle, or polygon. For example, a square expansion chamber can be constructed in order to provide better filling area and form factor concerns in electronic devices connected thereto, such as a cell phone or other hand held device including, for example, a MP3 player, a GPS (global positioning system) device, and/or a laptop.

As disclosed, the incorporation of the expandable chamber 116 can provide many advantages to the disclosed heat pipe 100. For example, as compared with a conventional heat pipe, the disclosed heat pipe can utilize an increased volume of working fluid (e.g., water or alcohol) to fill the heat pipe 100. In this case, more boiling of water can take place to provide more working capacity of the heat pipe. In another example, the pressure in the heat pipe 100 can be controlled and maintained at a desired level due to the addition of the expandable chamber in the heat pipe, as more and more water can be boiled in the heat pipe. In a further example, various cross sectional expandable/compressible shapes can be used to make the expandable chamber act as a heat sink element. For example, the expandable chamber can have a square cross section and can be constructed to provide better filling area and form factor concerns in electronic devices. The disclosed heat pipe can therefore be used as a heat sink cooled heat pipe that absorbs and dissipates heat from the electronic devices, e.g., using direct, radiant, or convective thermal contact. Further more, the disclosed heat pipe can provide flexibility in assembly. For example, the disclosed heat pipe can be bent around curves to fit the contours of any system, such as a video game system (not shown), while the pipe structure part of the heat pipe can be flattened to fit any flat-like surface of, e.g., the video game system. The compliance of the disclosed heat pipe can improve application flexibility.

Referring back to FIG. 1, the heat pipe 100 including the expandable chamber 116 can be made of a material with good heat conductivity. The expandable chamber 116 can provide control of the heat pipe internal pressure and/or the boiling point, and can therefore be used as, e.g., a vapor chamber to store the vapor therein; a pressure chamber to control the pressure therein; or a temperature chamber to expel the heat therein.

In operation, the working fluid such as water can be volatilized by heat transmitted or applied, e.g., from electronic components 180 at 120 of the heat pipe, to the evaporating section 112 (i.e., the heating section, or heat absorbing section), causing the water to boil at a preset temperature. The boiling temperature (or the boiling point) can be preset depending on features of the expandable chamber 116, for example, depending on the spring constant of an exemplary spring-type expandable vapor chamber. In various embodiments, the spring constant of the expandable pressure chamber can be adjusted such that the boiling temperature of the working fluid at “dry out” or a “complete evaporation” state is less than the maximum allowed case temperature, such as about 100° C.

As the water boils, the water vapor can occupy more space than liquid water along the pipe structure 124 and the expandable chamber 116 until the vapor fills pipe structure 124 and expandable chamber 116, which causes the pressure of the heat pipe 100 and the boiling temperature of the water to increase. When the water vapor fills the expandable chamber 116 of the heat pipe 100, the vapor chamber 116 can be expanded or unfolded, e.g., in a length direction 150 of FIG. 1, and the vapor can condense on the vapor chamber walls. The temperature of the expandable chamber 116 can then be decreased and heat can be released from the expandable chamber 116. The chamber 116 can be restored (or folded) to the equilibrium state to have a length close or equal to L₀ shown in FIG. 1, when releasing heat. Such vapor condensation and the heat releasing process can generate an under-pressure in the expandable chamber 116, which further conveys more vapor from the heat absorbing section 112 to the heat emitting section, i.e., the expandable chamber 116. Because of the capillary action of the capillary system 104, the condensed medium (e.g., water) can be pumped out of the expandable chamber and can continuously flow back to the heat absorbing section 112 of the heat pipe 100.

Various embodiments can also include a method for forming the disclosed heat pipe. For example, the heat pipe can be formed having a hollow metal casing that includes a pipe structure. In various embodiments, hollow metal casings and pipe structures that are known to one of ordinary skill in the art can be used for the disclosed heat pipe. The pipe structure can include an evaporating section for receiving heat at one end. An expandable chamber can be connected at the other end of the pipe structure in the hollow metal casing. Such expandable chamber can include a condensing section for releasing the heat that is received from the evaporating section of the pipe structure. A capillary system can then be arranged at an inner surface of the hollow metal casing to include the pipe structure and the expandable chamber.

The disclosed heat pipe 100 can be used in various applications. For example, the heat pipe 100 can be a vapor chamber cooler to allow water to be used to provide phase change cooling of a portable electronic device in a small, compact, passive (self-powered), and self-contained component.

In an exemplary embodiment, electronic devices can be packaged with the disclosed heat pipe to enable a high level of power to be dissipated. That is, the disclosed heat pipe can be an enabler for high power stacked components. For example, at 120 as shown in FIG. 1, a package stack of electronic devices 180 can be attached to the pipe structure 124 to dissipate the heat generated by the electronic device, such as a cell phone. In this case, the quantity of water can be adjusted such that water dries out or completely evaporates at the maximum power for the maximum length of the cell phone call or other operation.

The use of the disclosed heat pipe can also provide many advantages to the attached electronic devices. For example, more heat storage capacity can be provided as compared with conventional phase change solutions, e.g., using paraffin or salts. This is because the use of water can provide a 10 times higher heat of vaporization. In addition, the disclosed heat pipe can allow a higher working volume of water as compared with a conventional heat pipe due to use of the expandable chamber, which allows more heat to be absorbed in phase change and more heat dissipation through boiling. Further, the disclosed heat pipe having expandable chamber can be used as heat sink cooled heat pipe. Furthermore, the disclosed heat pipe can be very compact to enable cooling in, e.g., cell phones or other handheld applications. Even further, the disclosed heat pipe device can be an enabler for high density stacked die components.

Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. Moreover, all ranges disclosed herein are to be understood to encompass any and all sub-ranges subsumed therein. For example, a range of “less than 10” can include any and all sub-ranges between (and including) the minimum value of zero and the maximum value of 10, that is, any and all sub-ranges having a minimum value of equal to or greater than zero and a maximum value of equal to or less than 10, e.g., 1 to 5. In certain cases, the numerical values as stated for the parameter can take on negative values. In this case, the example value of range stated as “less than 10” can assume values as defined earlier plus negative values, e.g. −1, −1.2, −1.89, −2, −2.5, −3, −10, −20, −30, etc.

While the invention has been illustrated with respect to one or more implementations, alterations and/or modifications can be made to the illustrated examples without departing from the spirit and scope of the appended claims. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular function. Furthermore, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.” As used herein, the term “one or more of” with respect to a listing of items such as, for example, A and B, means A alone, B alone, or A and B. The term “at least one of” is used to mean one or more of the listed items can be selected.

Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims. 

1. A heat pipe comprising: a hollow metal casing comprising a pipe structure and an expandable chamber connected to a first end of the pipe structure, wherein the expandable chamber is configured to change in volume to control one or both of a temperature and a pressure in the hollow metal casing; and a capillary system disposed at an inner surface of the pipe structure and the expandable chamber.
 2. The heat pipe of claim 1, wherein the expandable chamber comprises one or more flexible corrugations so that the volume of the expandable chamber is changed by folding or unfolding the one or more flexible corrugations.
 3. The heat pipe of claim 1, wherein the expandable chamber comprises a spring-type mechanism.
 4. The heat pipe of claim 3, wherein the spring-type mechanism comprises a non-linear expansion and a non-linear restoration.
 5. The heat pipe of claim 1, wherein the expandable chamber comprises a cross sectional shape comprising a circle, a square, a rectangle, a triangle, or a polygon.
 6. The heat pipe of claim 1, further comprising a heat sink cooled heat pipe comprising the expandable chamber.
 7. The heat pipe of claim 1, further comprising a heat source at a second end of the pipe structure, wherein the second end of the pipe structure comprises an evaporating section for receiving heat from the heat source.
 8. The heat pipe of claim 7, wherein the heat source comprises a device within a cell phone, a MP3 device, a GPS device or a laptop computer.
 9. A heat pipe comprising: a pipe structure attached to an electronic device for receiving heat from the electronic device; and an expandable chamber connected to the pipe structure for dissipating the received heat through a phase change of water that flows through the pipe structure and the expandable chamber, wherein the expandable chamber is configured to change in volume so as to control one or both of a temperature and a pressure in the pipe structure.
 10. The heat pipe of claim 9, wherein the expandable chamber comprises one or more flexible corrugations so that the volume of the expandable chamber is changed by folding or unfolding the one or more flexible corrugations.
 11. The heat pipe of claim 9, wherein the expandable chamber comprises a linear spring-type mechanism or a non-linear spring-type mechanism so as to control one or both of the temperature and the pressure in the pipe structure.
 12. The heat pipe of claim 9, wherein the expandable chamber comprises a cross sectional shape comprising a circle, a square, a rectangle, a triangle, or a polygon.
 13. The heat pipe of claim 9, further comprising a heat sink cooled heat pipe comprising the expandable chamber.
 14. The heat pipe of claim 9, wherein the electronic device comprises a device within a cell phone, a MP3 device, a GPS device or a laptop computer.
 15. A method for forming a heat pipe comprising: providing a hollow metal casing comprising a pipe structure, wherein a first end of the pipe structure comprises an evaporating section for receiving heat; placing an expandable chamber in the hollow metal casing and connected at a second end of the pipe structure, wherein the expandable chamber comprises a condensing section for releasing the heat and is configured to change in volume to control one or both of a temperature and a pressure in the hollow metal casing; and arranging a capillary system at an inner surface of the pipe structure and the expandable chamber.
 16. The method of claim 15, wherein the volume of the expandable chamber is changed by folding or unfolding one or more flexible corrugations of the expandable chamber.
 17. The method of claim 15, wherein the expandable chamber comprises a linear spring-type mechanism or a non-linear spring-type mechanism so as to control one or both of the temperature and the pressure in the hollow metal casing.
 18. A method for dissipating heat comprising: providing a hollow metal casing comprising a pipe structure and an expandable chamber connected at a first end of the pipe structure; wherein the expandable chamber is configured to change in volume to control one or both of a temperature and a pressure in the hollow metal casing; packaging an electronic device at a second end of the pipe structure; and flowing a fluid in the hollow metal casing to receive heat transmitted from the electronic device and thereby generating a vapor that is condensed in the expandable chamber to release the heat.
 19. The method of claim 18, further comprising controlling a vapor pressure in the hollow metal casing by controlling an amount of the fluid flowing in the hollow metal casing.
 20. The method of claim 18, further comprising controlling a boiling temperature of the fluid flowing in the hollow metal casing by adjusting a spring constant of a spring-type expandable chamber.
 21. The method of claim 18, further comprising adjusting an amount of the fluid flowing in the hollow metal casing such that the fluid evaporates at a power for a maximum length of an operation of the electronic device.
 22. The method of claim 18, wherein the fluid flowing in the hollow metal casing comprises water, alcohol, or combinations thereof. 